The present invention relates to the production of perfluoropropane or octafluoropropane which is known to be useful in plasma etching of electronic components and is a dielectric gas.
The production of perfluoropropane has been attempted from a variety of starting materials, but no process has been developed which produces the material in high yields without a multitude of steps. Exemplary starting materials are propane, propene, hexafluoropropene and partially halogenated propanes and propenes.
U.S. Pat. No. 4,158,023 to von Halasz describes the production of perfluoropropane from hexafluoropropene in two steps. This reference indicates that the direct conversion with elemental fluorine results in poor yields. Since hexfluoropropene is itself fairly hard to produce in good yields, the overall process becomes involved with a multitude of steps and expense.
U.S. Pat. No. 3,840,445 to Paul et al. describes electrochemical fluorination of propane to perfluoropropane. The reference indicates the difficulty in separating propane from the product by distillation, and, accordingly, employs a two-step process of electrochemical fluorination. Although the product need be separated only from partially fluorinated propane when the two steps are used, the process thereby becomes more involved, and the potential for overall yield losses increases.
The production of perfluoropropane from propane by elemental fluorination in a jet reactor has been described in an article by A. F. Maxwell et al. in Journal of the American Chemical Society, Vol. 82, pp. 5827-30 (Nov. 20, 1960). The tables in this article report production of perfluoropropane which suggests a yield, in the best case, of about 50 percent based on propane fed.
Porous tube fluorinations are described in two applications filed herewith, which are not admitted to constitute prior art with respect to the present application. In the first application having the same inventorship as the present application Ser. No. 107,124 filed Dec. 26, 1979, fluorine-resistant fused alumina tubes are used for elemental fluorination of a variety of organic materials. In the other application having an additional coinventor Ser. No. 107,122 filed Dec. 26, 1979, a metal tube is used together with a perfluorinated diluent. Such applications describe a variety of details concerning suitable and preferred diluents, configurations, organic starting materials and other conditions suitable for the general reaction of organics with fluorine in such a reactor. The present invention is based upon the surprisingly good yields of perfluoropropane in either type of reactor from such diverse materials as propane, propene, and hexafluoropropene. Such results are believed to constitute an invention separate and apart from the more general application of either reaction to elemental fluorinations for a variety of materials, especially in view of the difficulties in producing perfluoropropane evidenced by the above-cited prior art.
A previous disclosure of Kurtz described in Canadian Pat. No. 990,738 and also in pending U.S. application Ser. No. 644,788, filed Dec. 29, 1975, commonly assigned now U.S. Pat. No. 4,187,253 issued Feb. 5, 1980, involves the chlorination of organics in similar reactors. Unlike the present fluorinations, chlorinations reported in Kurtz's disclosure appear to produce only partial chlorination of alkanes of more than one carbon.